Ion mobility spectrometer and method of analyzing ions

ABSTRACT

An ion mass spectrometer that has an ion channel shaped to modify the speed of a carrier gas as the carrier gas traverses the ion channel. In one case, the ion channel has segments of constant diameter in which the speed of the flowing gas is constant but different than the speed in other segments of the ion channel. This controlled variation in speed from segment to segment, together with the control of the axial electric field in the ion channel, provide greater control on the separation of ions in the ion channel. A method of analyzing ions based on a variation of at least one of axial electric field and of the speed of the flowing gas in the ion channel is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.16/969,358, filed Aug. 12, 2018, which is 371 application ofPCT/CA2019/050180, filed Feb. 13, 2019, which claims the benefit ofpriority of U.S. Provisional Patent Application No. 62/629,763, filedFeb. 13, 2018. U.S. application Ser. No. 16/969,358, PCT/CA2019/050180and U.S. Provisional Patent Application No. 62/629,763 are incorporatedherein by reference in their entirety.

FIELD OF THE INVENTION

The present disclosure relates to ion mobility spectrometry in generaland to trapped ion mobility spectrometry in particular. Moreparticularly, the present disclosure relates to an ion mobilityspectrometer and to a method of analyzing ions.

BACKGROUND OF THE INVENTION

Ion mobility spectrometry is a technique used to separate and identifyionized molecules in the gas phase based on their mobility in a flowingcarrier gas. There exist a number of variants to this method including,trapped ion mobility spectrometry in which a radio frequency (RF)electric field radially confines (traps) ions in an ion channel while aflowing carrier gas forces (drags) ions along the ion channel whilesimultaneously, an electric field exerts an electric force on the ions,in a direction opposite the direction followed by the flowing carriergas. The competing drag and electric forces act to separate the ions asa function of their mass to charge ratio and as a function of theircollisional cross-section.

Trapped ion mobility spectrometry remains limited with respect tocontrolling the linear velocity (speed) of the carrier gas in the ionchannel, the effectiveness of the RF field in radially confining theions along the center of the ion channel, and the control of theelectric field along the ion channel.

Therefore, improvements in ion mobility spectrometry are desirable.

SUMMARY OF THE DISCLOSURE

In a first aspect, the present invention provides an ion mobilityspectrometer that comprises an ion mobility analyzer, which has: a bodydefining an ion channel extending therethrough, the ion channel beingcontinuous, the ion channel having a diameter that varies monotonicallyalong the ion channel, the ion channel having an input section and anoutput section. The ion mobility analyzer further has: electrodes set inthe body, along the ion channel and around the ion channel, theelectrodes being arranged to receive an adjustable DC electrical signaland an adjustable time-varying electrical signal, the adjustable DCelectrical signal to generate an electric field along the ion channel,the time-varying electrical signal to generate a confining field toconfine ions in the ion channel along a central portion of the ionchannel, the central portion extending parallel to the ion channel.Additionally, the ion mobility analyzer has: an entrance guide coupledto the input section of the ion channel, the entrance guide configuredto guide ions to the ion channel. Furthermore, the ion mobility analyzerhas an exit guide coupled to the output section of the ion channel, theexit guide to guide ions exiting the analyzer out of the ion mobilityspectrometer. According to this aspect, the body can be made of anelectrically insulating material. Further, also according to thisaspect, the ion mobility spectrometer can also comprise an electricalsignal source coupled to the electrodes, the electrical signal sourcebeing configured to generate, in distinct linear segments of the ionchannel, distinct DC electric fields.

In a second aspect, the present disclosure provides an ion mobilityspectrometer that comprises: an analyzer, the analyzer having: a bodymade of a conductive material, the solid body defining an ion channelextending therethrough, the ion channel being continuous, the ionchannel having a diameter that varies monotonically along the ionchannel, the ion channel having an input section at a first end of thebody and an output section at a second end of the body, the conductivematerial being configured to generate a confining field to confine ionsin the ion channel along a central portion of the ion channel, thecentral portion extending parallel to the ion channel, the first end ofthe body and the second end of the body being configured to receive a DCvoltage to generate an electric field in the ion channel. The analyzerfurther has electrodes set in the body along the ion channel and aroundthe ion channel, the electrodes being arranged to receive an adjustabletime-varying electrical signal, the time-varying electrical signal togenerate a confining field to confine ions in the ion channel along acentral portion of the ion channel, the central portion extendingparallel to the ion channel, the electrodes being electrically isolatedfrom the body. The ion mobility further comprises an entrance guidecoupled to the input section of the ion channel, the entrance guideconfigured to guide ions to the ion channel; and an exit guide coupledto the output section of the ion channel, the exit guide to guide ionsexiting the analyzer out of the ion mobility spectrometer.

In relation to first and second aspects of the present disclosure:

In some embodiments, the electrodes protrude in the ion channel. Inother embodiments, the electrodes are flush with a wall of the ionchannel.

In some embodiments, the diameter of the ion channel decreasescontinuously from the input section to the output section. In somecases, the ion channel diameter decreases linearly from the inputsection to the output section. In other cases, the diameter of the ionchannel decreases quadratically from the input section to the outputsection. In yet other cases, the diameter of the ion channel decreasesquadratically from the input section to the output section.

In other embodiments, the diameter of the ion channel decreasescontinuously from the output section to the input section. In somecases, the ion channel diameter decreases linearly from the outputsection to the input section. In other cases, the diameter of the ionchannel decreases quadratically from the output section to the inputsection. In yet other cases, the diameter of the ion channel decreasesquadratically from the output section to the input section.

In certain embodiments, the ion channel includes a plurality of segmentseach having a respective constant diameter different from the diameterof the other segments of the plurality of segments. In theseembodiments, the ion channel includes one or more than one transitionsection, each segment of the plurality of segments is spaced apart fromanother segment of the plurality of segments by a respective one of theone or more than one transition section. In some cases, each transitionsection of the one or more than one transition section has a lengthparallel to the ion channel and a diameter that varies along the lengthof respective transition section.

In some embodiments, the ion mobility analyzer is such that theelectrodes are perpendicular to the ion channel and are radially alignedwith the ion channel. The electrodes can comprise groups of electrodes,each group of electrodes being in a respective plane that isperpendicular to the ion channel, each group of electrodes being spacedapart from the other groups of electrodes, along the ion channel. Eachgroup of electrodes can consists of an even number of electrodes. Theeven number can be six or twelve.

The entrance guide can be an entrance funnel and, the exit guide can bean exit funnel.

The time-varying electrical signal can be a radio frequency (RF)electrical signal. The RF electrical signal can be a multipole RFsignal.

The entrance guide can be configured to receive a flowing carrier gasand to provide the flowing carrier gas to the ion channel; and themonotonically varying diameter of the ion channel is configured to varya speed of the flowing carrier gas as the flowing carrier gas traversesthe ion channel. The ion spectrometer of the present disclosure canfurther comprise a source of carrier gas providing the flowing carriergas. The source of carrier gas can be a source of reagent carrier gas.Or, the ion mobility spectrometer can include a source of reagentcompound that provides the reagent compound for mixing with the flowingcarrier gas.

The body of the analyzer can be a monolithic body or a composite body.

In third aspect, the present invention provides a method of analyzingions, the method comprises: providing a flowing carrier gas to an ionchannel, the ion channel having an input section and an output section,the flowing carrier gas is input at the input section, the flowingcarrier gas containing the ions, the ion channel having a plurality ofsegments parallel to the ion channel, a speed of the flowing carrier gasbeing constant within each segment, the speed of the flowing carrier gasin a particular segment being different than the speed of the flowingcarrier gas in any other segment, the speed of the flowing carrier gaschanging monotonically along the ion channel, the flowing carrier gasgenerating a drag force on the ions, the drag force depending on thespeed of the flowing carrier gas. The method further comprises:generating an electric field in the ion channel to produce an electricforce acting on the ions, the electric force being in a directionopposite the direction of the drag force, the different speed of theflowing carrier gas in each segment of the ion channel and the electricforce resulting is a separation of the ions along the ion channel.Additionally, the method comprises varying at least one of an amplitudeof the electric field and the speed of the carrier gas in each segmentof the ion channel to eject ions from the output section of the ionchannel. In some embodiments, the method also comprises generating atime-varying electric field in the ion channel to confine the ions to acentral region of the ion channel. Additionally, the method can compriseaccumulating ions in the ion channel prior to varying at least one of anamplitude of the electric field and the speed of the carrier gas in eachsegment of the ion channel. The method can further comprise providingejected ions to an ion characterization device such as, for example, amass spectrometer. In further embodiments, the speed of the flowingcarrier gas is greater in a segment of the plurality of segments closestto the output section than the speed of the flowing carrier gas in asegment of the plurality of segments closest to the input section. Otheraspects and features of the present invention will become apparent tothose ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures.

FIG. 1 shows a side, cross-sectional view of an embodiment of an ionmobility spectrometer (IMS) in accordance with the present disclosure.

FIG. 2 shows a plot of the diameter of the ion channel of the IMS ofFIG. 1 , as a function of the length of the ion channel.

FIG. 3 shows an end view of the body of the IMS of FIG. 1 , taken fromthe input section side.

FIG. 4 shows a cross-section of the analyzer of the IMS of FIG. 1 with agroup of electrodes set in the body 38.

FIG. 5 shows the same cross-section of the analyzer as in FIG. 4 , butwith indications of where, on the group of electrodes, a DC electricalsignal can be provided and where a time-varying electrical signal can beprovided.

FIG. 6 shows a top perspective view of the body of the IMS of FIG. 1 ,with the apertures in which electrodes can be set.

FIG. 7 shows the radial dependence of a multipole field for differentorders of multipoles.

FIG. 8 shows examples of plots of electric fields that can be applied inthe IMS of FIG. 1 .

FIG. 9 shows an end view of the entrance guide of the IMS of FIG. 1 .

FIG. 10 shows a segment of the entrance guide of FIG. 9 , divided ineight sections configured to receive either a DC electrical signal or anAC electrical signal

FIG. 11 shows a segment of the exit guide of the IMS of FIG. 1 , dividedin eight sections configured to receive either a DC electrical signal oran AC electrical signal.

FIG. 12 shows another embodiment of the IMS of the present disclosure.

FIG. 13 shows a plot of the diameter of the ion channel of the IMS ofFIG. 12 , as a function of the length of the ion channel.

FIG. 14 shows a further embodiment of the IMS of the present disclosure.

FIG. 15 shows a plot of the diameter of the ion channel of the IMS ofFIG. 14 , as a function of the length of the ion channel.

FIG. 16 shows an additional embodiment of the IMS of the presentdisclosure.

FIG. 17 shows a plot of the diameter of the ion channel of the IMS ofFIG. 14 , as a function of the length of the ion channel.

FIG. 18 shows a flowchart of an embodiment of a method in accordancewith the present disclosure.

DETAILED DESCRIPTION

Generally, the present invention provides an ion mass spectrometer thathas an ion channel shaped to modify the speed of a carrier gas as thecarrier gas traverses the ion channel. In one case, the ion channel hassegments of constant diameter in which the speed of the flowing gas isconstant but different than the speed in other segments of the ionchannel. This controlled variation in speed from segment to segment,together with the control of the axial electric field in the ionchannel, together provide greater control on the separation of ions inthe ion channel. Within the context of the present disclosure, theexpression “linear velocity” is to be understood as meaning “linearspeed” or simply “speed”.

FIG. 1 shows a side, cross-sectional view of an embodiment of an ionmobility spectrometer (IMS) 20 in accordance with the presentdisclosure. The IMS 20 is connected to an ion source 24 that providesions to be analyzed to the IMS 20. Any suitable type of ion source canbe used without departing from the scope of the present disclosure. Forexample, an electrospray ionization source can be used. Other types ofion sources include: a laser ablation ion source, a sputtering ionsource, a discharge ion source, an inductively coupled plasma ionsource, a matrix-assisted laser desorption/ionization ion source, etc.

The IMS 20 has an entrance guide 30, which is configured to guide theions provided by the ion source 24 to an analyzer 32. The analyzer 32 iscoupled to an exit guide 34, which is configured to output the ionsanalyzed by the analyzer 32 outside the IMS 20. The ions output from theexit guide 34 can be provided or coupled to, for example, a massspectrometer, a Faraday cage, an electron multiplier, a photomultiplier,etc.

In the analyzer 32 of the present embodiment, the analyzer 32 has a body38, made of an electrically insulating material that defines an ionchannel 40, which extends through the body 38 from an input section 37to an output section 39. The ion channel 40 has a diameter that, ratherthan being constant along the entire length of the ion channel 40,varies monotonically along the ion channel 40. In this example, theanalyzer 32 has four segments 42A, 42B, 42C and 42D that each has aconstant diameter different than the diameter of the other segments.Separating the segments 42A, 42B, 42C and 42D from each other aretransition sections 44A, 44B and 44C, which each have a diameter thatvaries along the length the respective transition section.

Then analyzer can be of any suitable dimensions. For example, in someembodiments, the length of the analyzer can be about 120 mm. The lengthof the segments 42A, 42B, 42C and 42D can be 28 mm each, the length oftransition sections 44A, 44B and 44C can be 2 mm each, and the width canbe 34 mm. The diameter of segments 42A, 42B, 42C and 42D can be 14 mm,12 mm, 10 mm and 8 mm respectively. In other embodiments, the IMS 20 canbe miniature IMS fabricated using 3D printing. In other embodiments, theanalyzer can be manufactured using 3D printing technology. In suchembodiments, the analyzer can be manufactured as a body out of a poorlyconductive material, so that an application of a potential difference(voltage) between the ends of the analyzer generates a DC electric fieldalong the ion channel defined by the body. Examples of such poorlyconductive materials include carbon, metal-loaded plastics,nanoparticles composites, etc. In such embodiments, the electrodes setin the body 38 are electrically isolated from the body 38 by, forexample, providing an insulating material between the electrodes and thebody.

FIG. 2 shows an example of a plot of the diameter of the ion channel 40as a function of the length of the ion channel 40. In every lengthwiseportion of the ion channel, the diameter is either constant ordecreasing, which is akin to a monotonic decreasing function. As such,the ion channel 40 has a diameter that varies monotonically along theion channel 40. FIG. 2 also show a plot of the linear velocity of theflowing gas in each segment of the ion channel.

Returning to FIG. 1 , the IMS 20 has a carrier gas inlet 26 and acarrier gas outlet 28. The carrier gas inlet in coupled to a carrier gassource 22. The pressure at the carrier gas inlet 26 is greater than thepressure at the carrier gas outlet 28. This difference in pressurecauses the carrier gas to flow through the ion entrance guide 30, theion channel 40 and the ion exit guide 34, in the direction indicated bythe arrow 36. The analyzer 32 further includes electrodes 46, which arediscussed in detail further below. In general, the carrier gas can beun-reactive (for example, nitrogen, argon, etc.). However, any suitablecarrier gas can be used. In some embodiments, reagent gases can be usedto cause a chemical transformation of the ions being analyzed. In caseswhere dissimilar ions have the same mass to charge ratio and aredifficult to differentiate, adding a reagent gas can result in modifiedions that have different mobilities and that are more easilydistinguishable than the pre-reaction ions. The reagent gas can includeany suitable carrier gas to which reagent compounds are added. In somecases, the carrier gas can be reagent in itself. In other cases, thecarrier gas can be water vapor, methanol, acetonitrile, etc. As will beunderstood by the skilled worker, the carrier gas, reagent gas andreagent compounds can be selected in accordance with the particularchemical properties of the ions being analyzed. In cases where thecarrier gas is not by itself a reagent gas, reagent compounds can beadded to the carrier gas in any suitable way. For example, reagentcompounds can be added to the carrier gas source 22. Alternatively, thereagent compound can be provided by the ion source 24 in order to mixwith the carrier gas prior to the gas traversing the ion channel 40. Inother cases, a reagent compound source 23 can be coupled to IMS 20 andconfigured to provide reagent compounds to the IMS 20 in order for thereagent compounds to mix with the carrier gas prior to the gastraversing the ion channel 40.

In order to have a laminar flow of the carrier gas in the ion channel40, and to minimize/avoid any turbulent flow of the carrier gas, thetransition regions 44A, 44B and 44C are slopped from one segment to thenext. The shape of the slope can be linear, as shown in FIG. 1 , or canbe curved. For example, the curve in the transition region can besimilar to that of one side of a de Laval nozzle such that the thermalenergy of the gas is more efficiently converted into kinetic energyalong the flow axis. A sigmoidal curve or similar embodiment could alsobe an option.

FIG. 3 shows an end view of the body 38, taken from the input sectionside 37. The transition sections 44A, 44B and 44C are shown in thefigure. The cross-section shown in FIG. 3 is perpendicular to the ionchannel 40 and is, in the present example, dodecagonal. However, anysuitable cross-section is to be considered within the scope of thepresent disclosure. For example, instead of a dodecagonal cross-section,the body 38 can have, perpendicular to the ion channel 40, a circularcross-section, a square cross-section, a hexagonal cross-section, etc.The electrodes 46 are not shown in FIG. 3 .

Returning to FIG. 1 , as the segments 42A, 42B, 42C and 42D havedecreasing diameters, the speed at which the carrier gas traverses thesegments 42A, 42B, 42C and 42D of the ion channel 40 will increase fromone segment to the next. Any ion in the ion channel 40 will consequentlymove faster as it passes from one segment of the ion channel 40 to thenext. Because of the moving carrier gas, any ion present in the ionchannel 40 will be subjected to a drag force that increases as the speed(linear velocity) of the carrier gas increases.

To counteract the drag force exerted by the carrier gas on the ionspresent in the ion channel 40, the analyzer 32 has electrodes 46 set inthe body 38. These electrodes are used to generate an electric fieldinside the ion channel 40. The electric field is to exert an electricforce on the ions in the ion channel 40, in a direction parallel to theion channel 40. The electric field is such that the electric forcepushes the ions in the direction opposed to the direction in which thecarrier gas flows in the ion channel 40.

The electrodes 46 are set along the ion channel 40 and around the ionchannel 40. For clarity purposes, FIG. 1 shows electrodes 46 set only atthe lower part of the ion channel.

FIG. 4 shows a cross-section of the analyzer 32 with a group ofelectrodes 46 set in the body 38, in segment 42A. In this embodiment,the twelve electrodes 46 of the group are radially aligned with to theion channel 40 and are all in a same plane, which is perpendicular tothe ion channel 40. Further, the electrodes 46 are angularly equi-spacedaround the diameter of the ion channel 40. As will be understood by theskilled worker, analyzers that have a different number of electrodes orin which the electrodes are arranged differently than in the embodimentof FIG. 4 are to be considered within the scope of the presentdisclosure. As shown in this figure, the protruding electrodes define acircle 47 that has a diameter smaller than the diameter of the segment42A.

FIG. 5 shows the same cross-section of the analyzer 32 as in FIG. 4 ,but with indications of where, on the group of electrodes, a DCelectrical signal can be provided and where a time-varying electricalsignal (e.g. AC(−) and AC(+)) can be provided. FIG. 6 shows a topperspective view of the body 38, with apertures 48. The electrodes 46are configured to be set in the apertures 48 of the body 38.

In the present example, when electrodes 46 are set in in the apertures48 of the body 38 of FIG. 6 , all the electrodes aligned with each otherand with the ion channel 40 are subjected to the same electrical signal,which is the DC electrical signal or the time-varying electrical signal.When the time-varying electrical signal is an ideal two-dimensionalmultipole radio frequency (RF) electrical signal, the signal (V) can beexpressed, in polar coordinates, as:

${V( {r,\phi,t} )} = {V_{0}{\cos( {n\;\phi} )}( \frac{r}{R_{0}} )^{n}{\sin( {\omega t} )}}$

Where V₀ is the RF amplitude, R₀ is the inscribed radius of the RFelectrodes, and co denotes the angular frequency. V₀ can have a value ofa few hundreds of volts; in some embodiments, V₀ will not exceed 300volts. R₀ can be of the order of 1 MHz or, as will be understood by theskilled worker, depending of the configuration of the analyzer, can haveany other suitable value. “r” is the radial coordinate and “ϕ” is theangular coordinate. As will be understood by the skilled worker, inpractice, the RF signal is created by 2 n electrodes (i.e., for aquadrupolar field n=2, for a hexapolar field n=3, and so on). The radialdependence of the above described electric potential is plotted in FIG.7 . With increasing n, the confining RF field remains flatter and closerto zero further from the ion channel center axis. In other words, byincreasing n, ions can occupy a larger near-zero field region near theion channel center axis. This increases the relative number of ionswhich can be loaded into the analyzer and decreases space-chargingeffects which might limit mobility resolution.

In segments of the analyzer 32, there can be groups of twelve electrodesdisposed as shown in FIG. 5 . As will be understood by the skilledworker, this need not be the case. For example, if the diameter of aparticular segment is sufficiently small to prevent reliably settingtwelve electrodes therein, then fewer than twelve electrodes can be set.For example, six electrodes can be set instead of twelve. In otherembodiments there can be more than twelve electrodes per group ofelectrodes.

In the present embodiment, the DC electrical signal provided to theelectrodes 46 can be different for each of the segments 42A, 42B, 42Cand 42D, as shown by plot 50 in the graph of FIG. 8 . This divides theanalyzer 32 into four sectors which can be controlled individually.Dividing the mobility analyzer into independent sectors facilitatesseveral new modes of operation. In the mode shown at plot 50, theanalyzer 32 is employed as a series of four parallel flow ion mobilitydevices. This enables multiple simultaneous instances of ion separationand isolation for multiplexing measurements or for pre-concentratinganalytes prior to detection (at a mass spectrometer for example). Ofnote, the variation of the speed along the ion channel 40 provides anadditional degree of tuning of the analyzer 32.

In other modes of operation, multiple sectors can be combined andutilized as a single parallel flow device. One may then employ a linearDC ramp across several sectors while taking advantage of variation ofthe speed of the carrier gas in the segments 42A, 42B, 42C and 42D (seeplot 56), or one can tune the voltages for the individual sectors toshape the electric field gradient across the device (e.g., approximatesquare root function in plot 54, or exponential function in plot 58).Further, it is possible to generate multiple shaped electric fieldsacross the device as is shown in plot 52.

FIG. 9 shows an end view of the entrance guide 30, which, in thisembodiment, is funnel shaped. The entrance guide comprises a pluralityof ring segments 60 concentrically aligned with each other, from thering segment having the largest aperture to the ring segment having thesmallest aperture. In the present embodiment, the exit guide 34 is, asthe entrance guide 30, funnel shaped and looks similar to the entranceguide 30 shown in FIG. 9 . The ion funnels of the entrance guide 30 andthe exit guide 34 have a decreasing orifice size and decreasing appliedvoltage from the point where the ions enter to where they exit. There isalso a dipolar RF applied between adjacent annular electrodes (i.e.longitudinal along the device axis). This acts as an ion lens, focusingions down to a smaller cross-section at the funnel exit, resulting inhigher ion transmission to the detector. The force applied by the funnelelectric field is in the same direction as the gas/ion flow. Also, whilethe ions are radially confined in the funnel, an operator can select themass range for confinement by tuning the voltages; when highermass-to-charge (m/z) ratio species are selected, low m/z iontrajectories become unstable and these species are lost/neutralized.

Within the analyzer, there is a radial RF field (not a longitudinal RFfield). This confines all m/z ions efficiently. By employing highermultipolar fields (for example, hexapole, octupole, etc.), thisgenerates a relatively large low-field volume in the center of theanalyzer 34 (the analyzer can also be referred to a mobility cell). Thisallows loading of the mobility cell with significantly more ions thanprior art mobility cells (prior art analyzers), and it mitigates theeffects of field-induced heating, which can lead to ion fragmentationthat has a confounding effect in molecular determination. The DC voltageapplied in the mobility cell (analyzer 34) opposes the direction ofion/gas flow. This, combined with the radial confinement, traps the ionsin the region where the force provided by the opposing DC fieldperfectly counteracts the force applied by the gas flow.

The funnel-like electrode arrangement within the mobility cell (analyzer34) is used to ensure that the electric field gradient matches the gasflow gradient throughout the mobility cell.

FIG. 10 shows a segment 60 of the entrance guide 30 divided in eightsections configured to receive either a DC electrical signal or an ACelectrical signal. FIG. 11 shows a segment 62 of the exit guide 30divided in eight sections configured to receive either a DC electricalsignal or an AC electrical signal.

FIG. 12 shows another embodiment of an IMS 20 in accordance with thepresent disclosure. The embodiment of the IMS 20 of FIG. 12 is similarto the embodiment shown in FIG. 1 , except that the orientation of theion channel 40 in FIG. 12 is opposite from the one in FIG. 1 .

FIG. 13 shows an example of a plot of the diameter of the ion channel 40as a function of the length of the ion channel 40 for the embodiment ofFIG. 13 . In every lengthwise portion of the ion channel, the diameteris either constant or increasing, which is akin to a monotonicincreasing function. As such, the ion channel 40 has a diameter thatvaries monotonically along the ion channel 40. FIG. 13 also show a plotof the linear velocity of the flowing gas in each segment of the ionchannel.

FIG. 14 shows another embodiment of an IMS 20 in accordance with thepresent disclosure. The embodiment of the IMS 20 of FIG. 14 is similarto the embodiment shown in FIG. 1 , except that the ion channel 40,rather than having segments of constant diameter, has an ion channel 40that that is continuously slopped.

FIG. 15 shows an example of a plot of the diameter of the ion channel 40as a function of the length of the ion channel 40 for the embodiment ofFIG. 14 . All along the ion channel 40, the diameter of the channelincreases, which is akin to a monotonic increasing function. As such,the ion channel 40 has a diameter that varies monotonically along theion channel 40. FIG. 15 also show a plot of the linear velocity of theflowing gas in the ion channel.

FIG. 16 shows another embodiment of an IMS 20 in accordance with thepresent disclosure. The embodiment of the IMS 20 of FIG. 16 is similarto the embodiment shown in FIG. 14 , except that the diameter of the ionchannel 40 is larger at the input section 37 than at the output section39.

FIG. 17 shows an example of a plot of the diameter of the ion channel 40as a function of the length of the ion channel 40 for the embodiment ofFIG. 16 . All along the ion channel 40, the diameter of the channeldecreases, which is akin to a monotonic increasing function. As such,the ion channel 40 has a diameter that varies monotonically along theion channel 40. FIG. 15 also show a plot of the linear velocity of theflowing gas in the ion channel.

In the embodiments of FIGS. 14 and 16 , the diameter of the ion channel40 varies linearly from the input section 37 to the output section 39.In other embodiment, the diameter of the ion channel could varyquadratically or in accordance with any other suitable function, fromthe input section 37 to the output section 39.

In all the embodiments disclosed herein, the electrodes 46 protrude inthe ion channel 40. This need not be the case. In other embodiments,instead of protruding in the ion channel 40, the electrodes 46 are flushwith the wall of the ion channel 40. In yet other embodiments, theelectrodes 46 protrude in the ion channel 40 but, the protruding portionof the electrodes 46 can be coated with any suitable insulator film. Anyembodiment that has electrodes set in the body 38 and that produces aconfining field along the central portion 41 of the ion channel 40 iswithin the scope of the present disclosure. The central portion 41 isshown in FIG. 1 and is centered around the central axis of the ionchannel 40. The central axis is collinear with the arrow 36.

Having the electrodes 46 flush with the ion channel 40 can improve thelaminar flow condition of the carrier gas. By covering the electrodes 46with a thin insulator film, they are protected fromcorrosion/degradation.

In all the embodiments presented above, the ion channel 40 is describedas being defined by a body 38. The body can be a monolithic body or, thebody can be made of multiple parts secured together to define the ionchannel. Such a body can be referred to as a composite body. Dependingon the embodiments, the body 38 can be made of an electricallyinsulating material or of conductive material.

Preferably, the electrodes 46 are highly conductive and relativelyinert. Gold or stainless steel are two options of material that can beused for the electrodes 46.

When the electrodes 46 set in the body 38 are not separated from thebody with an electrical insulator, the material used for the body 38 isan electrically insulating material such as, for example, a plastics(PEEK, PTFE, etc.) or machinable ceramics (for example, Macor™) aresuitable.

When the material of body 38 is made of an insulator material, DC andtime-varying electric fields can be applied by using the electrodes 46set in the body 38 as showed in the embodiment of FIG. 1 .Alternatively, the body of the ion channel can be made of conductivematerial of high resistivity. In such embodiments, passing DC currentthrough the body 38 will produce a DC voltage gradient along the ionchannel 40. The shape of the DC electric field along the channel willcorrespond to the resistance along the body of the ion channel 40. TheAC field can be introduced by embedded electrically isolated electrodesin the body of the ion channel or it can be introduced via an externalRF induction circuit coupled to the analyzer 34 and to the ion channel40. The latter approach can be better when attempting to generate an RFfield in the ion channel of a miniature analyzer produced by 3Dprinting.

FIG. 18 shows a flowchart of a method of analyzing ions in accordancewith the present disclosure. At step 100, a flowing carrier gas isprovided to an ion channel. The ion channel has an input section and anoutput section and the flowing carrier gas is input at the inputsection. The flowing carrier gas containing the ions. The ion channelhas a plurality of segments parallel to the ion channel and a speed ofthe flowing carrier gas is constant within each segment but, the speedof the flowing carrier gas in a particular segment is different than thespeed of the flowing carrier gas in any other segment of the ionchannel. The speed of the flowing carrier gas changes monotonicallyalong the ion channel. The flowing carrier gas generates a drag force onthe ions and the drag force depends on the speed of the flowing carriergas. Examples of such an ion channel are shown at FIGS. 1, 12, 14 and 16.

Returning to FIG. 18 , at step 102, an electric field is generated inthe ion channel to produce an electric force acting on the ions. Thefield is such that the electric force is in a direction opposite thedirection of the drag force. The different speed of the flowing carriergas in each segment of the ion channel and the electric force result isa separation of the ions along the ion channel.

At step 104, a variation of at least one of an amplitude of the electricfield and the speed of the carrier gas in each linear segment of the ionchannel is effected in order to eject ions from the output section ofthe ion channel.

Additionally, a step of generating a time-varying electric field in theion channel to confine the ions to a central region of the ion channelcan be performed. Further, ions can be accumulated ions in the ionchannel prior to varying at least one of an amplitude of the electricfield and the speed of the carrier gas in each segment of the ionchannel.

Further, the ejected ions can be provided to an ion characterizationdevice. For example, a mass spectrometer.

Furthermore, in some embodiments of the method, the form of the ionchannel can be such that the speed of the flowing carrier gas is greaterin a segment of the plurality of segments closest to the output sectionthan the speed of the flowing carrier gas in a segment of the pluralityof segments closest to the input section.

As detailed above, the present disclosure provides an ion massspectrometer that has an ion channel shaped to modify the speed of acarrier gas as the carrier gas traverses the ion channel. In one case,the ion channel has segments of constant diameter in which the speed ofthe flowing gas is constant but different than the speed in othersegments of the ion channel. The controlled variation in speed fromsegment to segment, together with the control of the axial electricfield in the ion channel, provide greater control on the separation ofions in the ion channel.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments of the invention. However, it will be apparent to oneskilled in the art that these specific details are not required in orderto practice the invention. In other instances, well-known electricalstructures and circuits are shown in block diagram form in order not toobscure the invention. For example, specific details are not provided asto whether the embodiments of the invention described herein areimplemented as a software routine, hardware circuit, firmware, or acombination thereof.

Embodiments of the invention can be represented as a software productstored in a machine-readable medium (also referred to as acomputer-readable medium, a processor-readable medium, or a computerusable medium having a computer-readable program code embodied therein).The machine-readable medium can be any suitable tangible medium,including magnetic, optical, or electrical storage medium including adiskette, compact disk read only memory (CD-ROM), memory device(volatile or non-volatile), or similar storage mechanism. Themachine-readable medium can contain various sets of instructions, codesequences, configuration information, or other data, which, whenexecuted, cause a processor to perform steps in a method according to anembodiment of the invention. Those of ordinary skill in the art willappreciate that other instructions and operations necessary to implementthe described invention can also be stored on the machine-readablemedium. Software running from the machine-readable medium can interfacewith circuitry to perform the described tasks.

The above-described embodiments of the invention are intended to beexamples only. Alterations, modifications and variations can be effectedto the particular embodiments by those of skill in the art withoutdeparting from the scope of the invention, which is defined solely bythe claims appended hereto.

What is claimed is:
 1. An ion mobility spectrometer comprising: ananalyzer, the analyzer having: a body made of a conductive material, thesolid body defining an ion channel extending therethrough, the ionchannel being continuous, the ion channel having a diameter that variesmonotonically along the ion channel, the ion channel having an inputsection at a first end of the body and an output section at a second endof the body, the first end of the body and the second end of the bodybeing configured to receive a DC voltage to generate an electric fieldin the ion channel; electrodes set in the body along the ion channel andaround the ion channel, the electrodes being arranged to receive anadjustable time-varying electrical signal, the time-varying electricalsignal to generate a confining field to confine ions in the ion channelalong a central portion of the ion channel, the central portionextending parallel to the ion channel, the electrodes being electricallyinsulated from the body; an entrance guide coupled to the input sectionof the ion channel, the entrance guide configured to guide ions to theion channel.
 2. The ion mobility spectrometer of claim 1, wherein theelectrodes protrude in the ion channel, or the electrodes are flush witha wall of the ion channel.
 3. The ion mobility spectrometer of claim 1,wherein the diameter of the ion channel decreases continuously from theinput section to the output section.
 4. The ion mobility spectrometer ofclaim 3, wherein the diameter of the ion channel decreases linearly fromthe input section to the output section, or decreases quadratically fromthe input section to the output section.
 5. The ion mobilityspectrometer of claim 1, wherein the diameter of the ion channeldecreases continuously from the output section to the input section. 6.The ion mobility spectrometer of claim 5, wherein the diameter of theion channel decreases linearly from the output section to the inputsection, or decreases quadratically from the output section to the inputsection.
 7. The ion mobility spectrometer of claim 1, wherein the ionchannel includes a plurality of segments each having a respectiveconstant diameter different from the diameter of the other segments ofthe plurality of segments.
 8. The ion mobility spectrometer of claim 7,wherein the ion channel includes one or more than one transitionsection, each segment of the plurality of segments is spaced apart fromanother segment of the plurality of segments by a respective one of theone or more than one transition section.
 9. The ion mobilityspectrometer of claim 8, wherein each transition section of the one ormore than one transition section has a length parallel to the ionchannel and a diameter that varies along the length of respectivetransition section.
 10. The ion mobility spectrometer of claim 1,wherein the electrodes are perpendicular to the ion channel and areradially aligned with the ion channel.
 11. The ion mobility spectrometerof claim 1, wherein the electrodes comprise groups of electrodes, eachgroup of electrodes being in a respective plane that is perpendicular tothe ion channel, each group of electrodes being spaced apart from theother groups of electrodes, along the ion channel.
 12. The ionspectrometer of claim 11, wherein each group of electrodes consists ofan even number of electrodes.
 13. The ion spectrometer of claim 1,wherein the entrance guide is an entrance funnel.
 14. The ionspectrometer of claim 1, wherein the time-varying electrical signal is aradio frequency (RF) signal.
 15. The ion spectrometer of claim 14,wherein the RF signal is a multipole RF signal.
 16. The ion spectrometerof claim 12, wherein the even number is six or twelve.
 17. The ionspectrometer of claim 1, wherein: the entrance guide is configured toreceive a flowing carrier gas and to provide the flowing carrier gas tothe ion channel; and the monotonically varying diameter of the ionchannel is configured to vary a speed of the flowing carrier gas as theflowing carrier gas traverses the ion channel.
 18. The ion spectrometerof claim 17, further comprising a source of carrier gas providing theflowing carrier gas.
 19. The ion spectrometer of claim 17, furthercomprising at least one of: a source of reagent compound configured toprovide the reagent compound to the flowing carrier gas, and a source ofreagent gas to provide the reagent gas to the flowing carrier gas. 20.The ion spectrometer of claim 1 further comprising an electrical signalsource coupled to the electrodes, the electrical signal source beingconfigured to generate, in distinct linear segments of the ion channel,distinct DC electric fields.